Pilot scale evaluation of SANI^® process for sludge minimization and greenhouse gas reduction in saline sewage treatment

This study reports on a pilot trial of the SANI^® process (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated process) in Hong Kong. A pilot-scale SANI plant treating saline sewage at 10 m³/day was scaled-up from a lab-scale system treating synthetic saline sewage. The plant consisted of a sulfate reduction up-flow sludge bed (SRUSB), an anoxic bioreactor (BAR1) for autotrophic denitrification utilizing dissolved sulfide produced by the SRUSB and an aerobic bioreactor (BAR2) for nitrification. The SANI^® pilot plant was successfully operated for 225 days and achieved average COD, TSS, TN removal of 87, 87, and 57%, respectively. The ratio of MLVSS to MLSS in the SRUSB was stable at 0.7 and the average sludge volume index (SVI) was constantly below 110 ml/g. No sludge was purposely withdrawn from the plant during 225-day plant operation. This was attributed to a very low observed sludge yield (0.02 kgVSS/kgCOD removed) of the SRUSB reactor. DNA extraction, PCA amplification results revealed that no methanogens were detected in the SRUSB. SANI^® can reduce 90% sludge production, 35% energy and 36% GHG compared to conventional biological nutrient removal (CBNR) process.